How Body Fat Percentage is Estimated — The U.S. Navy Method

BMI tells you weight relative to height. Body fat percentage tells you something more useful: how much of your mass is actually fat versus lean tissue. The U.S. Navy developed a circumference-based method that’s surprisingly accurate without expensive equipment.

What you need to measure

Men: Neck circumference + Waist circumference + Height
Women: Neck + Waist + Hip circumference + Height

All measurements in centimetres, taken on bare skin with a flexible tape.

Where to measure

• Neck: Narrowest point, just below the Adam’s apple
• Waist: At the navel (belly button level) for men; at the natural waist (narrowest point) for women
• Hip: Widest point of the buttocks (women only)

The formula

Male:
BF% = 495 / (1.0324 − 0.19077×log₁₀(waist−neck) + 0.15456×log₁₀(height)) − 450

Female:
BF% = 495 / (1.29579 − 0.35004×log₁₀(waist+hip−neck) + 0.22100×log₁₀(height)) − 450

The logarithmic functions account for the non-linear relationship between circumference and actual fat storage.

Body fat categories

Category	Men	Women
Essential fat	2–5%	10–13%
Athletic	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Obese	25%+	32%+

Women naturally carry more essential fat (for hormonal and reproductive function). This is why the scales differ.

How accurate is it?

Studies show the Navy method is within ±3–4% of DEXA scans for most adults. It works best for people with typical body proportions. It’s less accurate for very lean athletes or people with unusual fat distribution.

Body fat vs BMI

A muscular person with 12% body fat might have a BMI of 28 (classified “overweight”). Body fat percentage reveals what BMI hides: they’re extremely fit. Conversely, a person with normal BMI but 30% body fat (skinny-fat) faces metabolic risks that BMI doesn’t flag.

How to use the result

• Track monthly to see trends from training/diet changes
• Don’t obsess over ±1% — measurement variability is normal
• Combine with waist circumference for a fuller picture
• Consult a professional before making health decisions based on estimates

Estimate yours with the OurDailyCalc body fat calculator.

TL;DR

• Navy method uses circumference measurements + height
• Men need neck + waist; women need neck + waist + hip
• Accuracy: ±3–4% vs DEXA for most adults
• More meaningful than BMI for assessing health, especially for athletic people